Add Arch packaging and Forgejo workflows for bakery

- packaging/arch/PKGBUILD: builds the bakery CLI from the workspace
- .forgejo/workflows/package.yml: publishes to the [breadway] Arch registry on tag
- .forgejo/workflows/mirror.yml: mirrors to GitHub

.forgejo/workflows/mirror.yml

@@ -0,0 +1,21 @@
+name: Mirror to GitHub
+
+on:
+  push:
+    branches: ['**']
+    tags: ['**']
+
+jobs:
+  mirror:
+    runs-on: [self-hosted, hestia]
+    steps:
+      - name: Mirror to GitHub
+        run: |
+          set -euo pipefail
+          git clone --mirror "https://git.breadway.dev/${GITHUB_REPOSITORY}.git" repo.git
+          cd repo.git
+          # Mirror only branches and tags (not refs/pull/*, which GitHub rejects);
+          # --prune deletes GitHub refs that no longer exist on Forgejo.
+          git push --prune \
+            "https://x-access-token:${{ secrets.MIRROR_TOKEN }}@github.com/Breadway/bread-ecosystem.git" \
+            '+refs/heads/*:refs/heads/*' '+refs/tags/*:refs/tags/*'